1. Field of the Invention
The present invention relates to a substrate treatment apparatus and a substrate treatment method for treating a substrate with a treatment liquid. Examples of the substrate to be treated include semiconductor wafers, substrates for liquid crystal display devices, substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks and substrates for photo masks.
2. Description of Related Art
In production processes for a semiconductor device and a liquid crystal display device, a substrate such as a semiconductor wafer or a glass substrate for the liquid crystal display device is treated with a treatment liquid. A substrate treatment apparatus of a single substrate treatment type adapted to treat a single substrate at a time includes, for example, a spin chuck which horizontally holds and rotates a substrate, and a nozzle which supplies a treatment liquid onto a major surface (treatment surface) of the substrate held by the spin chuck. Where the treatment liquid is supplied onto an upper surface of the substrate held by the spin chuck, the substrate is held by the spin chuck with its front surface (treatment surface) facing up. Then, the treatment liquid is supplied to a center portion of the front surface of the substrate from the nozzle, while the substrate is rotated by the spin chuck. The treatment liquid supplied to the front surface of the substrate receives a centrifugal force generated by the rotation of the substrate to spread from the center portion toward a peripheral edge of the substrate on the front surface of the substrate.
In order to reliably cover the entire upper surface of the substrate with the treatment liquid, the treatment liquid should be supplied to the substrate at a relatively high flow rate. This increases the amount of the treatment liquid required for the treatment of the single substrate, thereby correspondingly increasing the treatment costs.
A conceivable approach to this problem is, as disclosed in Japanese Unexamined Patent Publication No. 8 (1996)-78368, to provide an opposing member in closely opposed relation to the upper surface of the substrate to cover the entire upper surface for retaining a film of the treatment liquid between the opposing plate and the upper surface of the substrate while supplying the treatment liquid to the upper surface of the substrate. In this case, the film-forming treatment liquid spreads radially outward about a rotation center of the substrate in a space defined between the opposing plate and the substrate. Thus, the treatment liquid spreads over the entire upper surface of the substrate, so that a thin treatment liquid film can be retained on the entire upper surface.
In order to minimize the flow rate of the treatment liquid to be supplied to the substrate, the treatment liquid film to be formed on the upper surface of the substrate desirably has the smallest possible thickness. That is, the opposing plate is desirably spaced the smallest possible distance from the upper surface of the substrate.
However, there is a possibility that the substrate vertically wobbles during the rotation of the substrate. Even if an attempt is made to place the opposing plate in closely opposed relation to the substrate, there is a limitation in the distance between the opposing plate and the substrate. More specifically, an attempt to maintain the distance between the opposing plate and the substrate to several tenths of millimeters is likely to fail due to the vertical wobbling of the substrate. As a result of variations in the distance between the opposing plate and the substrate, the thin liquid film present between the opposing plate and the upper surface of the substrate is liable to become discontinuous, making it impossible to keep covering the upper surface of the substrate.
Where the treatment liquid is to be supplied to a lower surface of the substrate held by the spin chuck, a center axis nozzle is used which is inserted through a rotation shaft of the spin chuck. The center axis nozzle has an outlet port provided at an upper end thereof, and the outlet port is opposed to a center portion of the lower surface of the substrate held by the spin chuck.
The substrate is held by the spin chuck with its front surface (treatment surface) facing down. Then, the treatment liquid is spouted upward toward the center portion of the lower surface of the substrate from the outlet port, while the substrate is rotated by the spin chuck. The treatment liquid reaching the lower surface of the substrate receives a centrifugal force generated by the rotation of the substrate to flow from the center portion toward the peripheral edge on the lower surface of the substrate. Thus, the treatment liquid spreads over the entire lower surface of the substrate.
In order to reliably cover the entire lower surface of the substrate with the treatment liquid, the treatment liquid should be supplied to the substrate at a relatively high flow rate. This increases the amount of the treatment liquid required for the treatment of the single substrate, thereby correspondingly increasing the treatment costs.
A conceivable approach to this problem is to provide an opposing plate in closely opposed relation to the lower surface of the substrate to cover the entire lower surface for retaining a film of the treatment liquid between the opposing plate and the lower surface of the substrate while supplying the treatment liquid to the lower surface of the substrate. In this case, the film-forming treatment liquid spreads radially outward about the rotation center of the substrate in a space defined between the opposing plate and the substrate. Thus, the treatment liquid spreads over the entire lower surface of the substrate, so that a thin treatment liquid film can be retained on the entire lower surface.
However, there is a possibility that the opposing plate disposed in opposed relation to the lower surface of the substrate hinders a spin drying process which is performed on the substrate after the treatment of the substrate with the treatment liquid. The spin drying process is such that the treatment liquid adhering to the substrate is spun out by a centrifugal force generated by rotating the substrate at a higher rotation speed. In the spin drying process, a turbulent flow is liable to occur in the space between the opposing plate and the lower surface of the substrate, resulting in unsatisfactory drying of the substrate.